The invention relates to an apparatus for feeding a rock drilling machine in extension rod drilling, comprising at least one feeding cylinder and a piston provided with a two-sided piston rod, and pressure fluid conduits for feeding pressure fluid into pressure fluid spaces in the feeding cylinder and away therefrom, the feeding cylinder being mounted in the feeding apparatus in such a way that the piston is longitudinally immovable with respect to the feeding apparatus and the feeding cylinder is movable in the feeding direction with respect to the piston; a second piston immovable in the longitudinal direction of the feeding cylinder and a separate connecting cylinder displaceable in the longitudinal direction of the feeding cylinder with respect to the second piston and the feeding cylinder, said second piston and said connecting cylinder being arranged around the feeding cylinder; and pressure fluid conduits separate from the pressure fluid conduits of the feeding cylinder for feeding pressure fluid into the pressure fluid spaces in the connecting cylinder to the different sides of the second piston for displacing the connecting cylinder with respect on feeding cylinder, the drilling machine being connected to the connecting cylinder.
In long-hole or extension rod drilling, several drill rods or pipes are attached to each other in succession to achieve the desired drill hole length. Successive drill rods or pipes are interconnected by means of threads. In order to add a new drill rod or pipe, the drilling machine is detached from the preceding drill rods and the new rod is positioned therebetween and fastened by rotating the drilling machine. In the prior art arrangements the drilling machine is displaced by the same feeding device both during the drilling process and when attaching or detaching drill rods or pipes. The feeding device displaces the drilling machine in a desired direction, depending on whether a new rod is to be attached to or detached from the drill string. A problem therewith is that the length of the displacing movement cannot be adjusted when closing or opening threads as there are no provisions for such adjustment. One well-known solution to the problem is to use various sensors which detect the movements of the drilling machine with respect to the feeding beam. In automatic and computer-controlled drilling in particular, the required sensing operations cause extra work in terms of control and required connections in order to ensure successful drilling. Long-hole drilling equipments generally comprise a hydraulic telescope cylinder provided with a rod or pipe fixed in the direction of travel of the drilling machine, a displacing cylinder connected to the drilling machine being movable on this rod or pipe. It is known to use in the feeding apparatus telescopically interconnected displacing cylinders comprising several superimposed cylinders so connected that they all move simultaneously when pressure fluid is fed. This kind of arrangement is known from SE Published Specification 311130, which discloses two different embodiments of the telescope cylinder. In these embodiments, the drilling machine is displaced in its longitudinal direction by feeding pressure fluid through one feed conduit into cylinder spaces within the structure of the telescope cylinder, so that all the cylinders move simultaneously, whereby the cylinder construction is extended, or when pressure fluid is fed into the other pressure fluid conduit, the cylinder construction is shortened.
A similar arrangement is disclosed in FI Patent Application 852051, in which two cylinders are positioned one upon the other on a fixed arm. When pressure fluid is fed through pressure fluid conduits formed in the fixed arm and conduits formed in the cylinders, both cylinders move simultaneously in either direction, depending on through which end of the fixed arm the pressure fluid is fed.